Blank cartridge

A blank cartridge comprising:

• a cartridge casing with a first primer;
• a piston with a head and an arm;
• and
• an expansion chamber located between said primer and the head of the piston;
• wherein, following detonation of the primer, the piston slidably displaces substantially within the casing of said cartridge;
• and
• wherein, prior to firing, the front of the cartridge forms between the casing and the piston a recessed portion;
• whereby the front of the casing can fit around a projection formed in the breech of a gun and, following detonation, during expansion, the piston's arm abuts against the projection to tend to oust the cartridge from the breech.